Fix for arithmetic side effect

pallets/limit-orders/src/lib.rs

@@ -346,6 +346,8 @@ pub mod pallet {
         /// Call on_runtime_upgrade or wait for genesis to complete registration
         /// before enabling the pallet.
         PalletHotkeyNotRegistered,
+        /// A TAO -> alpha conversion overflowed the fixed-point range.
+        ArithmeticOverflow,
     }
 
     // ── Hooks ─────────────────────────────────────────────────────────────────
@@ -867,7 +869,7 @@ pub mod pallet {
                 total_sell_net,
                 total_sell_tao_equiv,
                 current_price,
-            );
+            )?;
             Self::deposit_event(Event::GroupExecutionSummary {
                 netuid,
                 net_side,
@@ -1015,7 +1017,7 @@ pub mod pallet {
                 };
                 Ok((OrderSide::Buy, actual_alpha))
             } else {
-                let total_buy_alpha_equiv = Self::tao_to_alpha(total_buy_net, current_price);
+                let total_buy_alpha_equiv = Self::tao_to_alpha(total_buy_net, current_price)?;
                 let net_alpha = (total_sell_net.saturating_sub(total_buy_alpha_equiv)) as u64;
                 let actual_tao = if net_alpha > 0 {
                     let out = T::SwapInterface::sell_alpha(
@@ -1054,7 +1056,7 @@ pub mod pallet {
         ) -> DispatchResult {
             let total_alpha: u128 = match net_side {
                 OrderSide::Buy => actual_out.saturating_add(total_sell_net),
-                OrderSide::Sell => Self::tao_to_alpha(total_buy_net, current_price),
+                OrderSide::Sell => Self::tao_to_alpha(total_buy_net, current_price)?,
             };
 
             for e in buys.iter() {
@@ -1206,30 +1208,35 @@ pub mod pallet {
             total_sell_net: u128,
             total_sell_tao_equiv: u128,
             current_price: U96F32,
-        ) -> u64 {
+        ) -> Result<u64, DispatchError> {
             match net_side {
-                OrderSide::Buy => (total_buy_net.saturating_sub(total_sell_tao_equiv)) as u64,
+                OrderSide::Buy => Ok((total_buy_net.saturating_sub(total_sell_tao_equiv)) as u64),
                 OrderSide::Sell => {
-                    let buy_alpha_equiv = Self::tao_to_alpha(total_buy_net, current_price) as u64;
-                    (total_sell_net as u64).saturating_sub(buy_alpha_equiv)
+                    let buy_alpha_equiv = Self::tao_to_alpha(total_buy_net, current_price)? as u64;
+                    Ok((total_sell_net as u64).saturating_sub(buy_alpha_equiv))
                 }
             }
         }
 
         /// Convert a TAO amount to alpha at `price` (TAO/alpha).
-        /// Returns 0 when `price` is zero.
-        #[allow(clippy::arithmetic_side_effects)]
-        fn tao_to_alpha(tao: u128, price: U96F32) -> u128 {
+        ///
+        /// A zero `price` yields `Ok(0)` (no alpha is purchasable). A genuine
+        /// fixed-point overflow returns `Err(ArithmeticOverflow)` so the caller
+        /// aborts the batch.
+        fn tao_to_alpha(tao: u128, price: U96F32) -> Result<u128, DispatchError> {
             if price == U96F32::from_num(0u32) {
-                return 0u128;
+                return Ok(0u128);
             }
-            (U96F32::from_num(tao) / price).saturating_to_num::<u128>()
+            U96F32::saturating_from_num(tao)
+                .checked_div(price)
+                .map(|alpha| alpha.saturating_to_num::<u128>())
+                .ok_or(Error::<T>::ArithmeticOverflow.into())
         }
 
         /// Convert an alpha amount to TAO at `price` (TAO/alpha).
         fn alpha_to_tao(alpha: u128, price: U96F32) -> u128 {
             price
-                .saturating_mul(U96F32::from_num(alpha))
+                .saturating_mul(U96F32::saturating_from_num(alpha))
                 .saturating_to_num::<u128>()
         }
     }

pallets/limit-orders/src/tests/auxiliary.rs

@@ -31,7 +31,8 @@ fn net_amount_for_event_buy_dominant() {
             150u128,   // total_sell_net (alpha)  ← not used in Buy branch
             300u128,   // total_sell_tao_equiv
             price,
-        );
+        )
+        .expect("conversion does not overflow");
         assert_eq!(net, 700u64);
     });
 }
@@ -48,7 +49,8 @@ fn net_amount_for_event_sell_dominant() {
             500u128, // total_sell_net (alpha)
             400u128, // total_sell_tao_equiv (not used in Sell branch directly)
             price,
-        );
+        )
+        .expect("conversion does not overflow");
         // buy_alpha_equiv = 200 / 2 = 100; net = 500 - 100 = 400
         assert_eq!(net, 400u64);
     });
@@ -65,7 +67,8 @@ fn net_amount_for_event_perfectly_offset() {
             100u128,
             200u128,
             price,
-        );
+        )
+        .expect("conversion does not overflow");
         assert_eq!(net, 0u64);
     });
 }